Pressure Vessels - Engineer’s Survival Kit

Today, a pressure vessel (cylindrical or spherical) is designed to hold liquids or gases at a pressure substantially higher than the ambient pressure. The soda can is considered a thin wall pressure vessel model. In a thin wall pressure vessel, we measure two stresses: the longitudinal stress and the hoop stress.

Determining the pressure of the fluids contained within an aluminum beverage can makes an inexpensive laboratory experiment utilizing strain gage technology.

The Micro-Measurements strain gage rosette sensor plays a most important role. The rosette allows the stress analyst to minimize the number of qualifying assumptions made. Without the use of a full-field technique, the problem of locating the rosette at the stress concentration remains.

But when a three element rosette is used, no assumption of the uniaxial stress state ever needs to be made. Since the rosette is usually installed on a free surface subjected only to low hydrostatic pressure of the surrounding air and minimal body forces in the normal direction, the safer assumption of the biaxial stress state can readily be made of the stresses present on the surface.

And when a three element rosette is used, no assumption about the reactions of the principal strains and stresses ever needs to be made. The rosette can be installed without regard to the orientation.

Using the three strains subsequently measured by the three elements of rosette, the two principle strains – and their direction- can be readily calculated. And, of course, if the material properties are known, the principle stresses can then be determined (even if one of them just happens to be zero).